The long range goal of this research is to elucidate the pathogenesis of immune complex glomerulonephritis. A well-described rat model of chronic serum sickness will be studied. In the model, nephritis progresses in three stages (Mild, Moderate, Severe) that can be unequivocally distinguished by criteria of kidney function or immunopathology. Transitions from stage to stage occur as relatively sudden, discrete events. Since glomerular hypercellularity in Severe chronic serum sickness is largely attributable to phenotypically abnormal macrophages, it has been proposed that secretory and/or metabolic activities of those macrophages could account for much of the pathophysiology and immunopathology unique to the Severe stage. Hallmarks include capillary obliteration, necrosis and sclerosis, declining kidney function, severe proteinuria, with cachexia, and urinary excretion of tumor necrosis factor-alpha (TNF). To determine whether macrophage activation in Severe chronic serum sickness differs significantly from earlier stages, glomerular expression of genes for the macrophage inflammatory mediators, TNF and interleukin-1Beta (IL-1) will be evaluated by means of Northern and dot blot analysis of extracted mRNA and by in situ hybridization. In addition, in situ hybridization will be combined with immunohistochemistry to 1) identify the phenotype of macrophages expressing cytokine genes, 2) establish whether other glomerular cells express those genes, and 3) document cellular changes in gene expression that might be relevant for disease progression. Direct measurements of cytokine secretion will be made to detect differences in cytokine synthesis between Severe chronic serum sickness and earlier stages. The capacity of isolated glomeruli to secrete TNF and IL-1 will be measured in vitro. To assess the contribution of macrophages to that secretion, isolated glomerular cells will be similarly tested, before and after macrophage depletion. Other aspects of macrophage function that might distinguish Moderate and Severe stages will also be examined, including phagocytosis, spreading, and superoxide anion generation.. The possibility that glomerular T cells may contribute to local macrophage activation will be investigated by studying surface marker expression and some functional properties of those T cells. These studies could lead to improvements in monitoring human proliferative immune complex nephropathies and to new approaches for the treatment of those life-threatening diseases.